Bipolar disorder and severe premenstrual syndrome (PMS) have many symptoms in common, but it is important to establish the correct diagnosis between a severe psychiatric disorder and an endocrine disorder appropriately treatable with hormones.

The measurement of hormone levels is not helpful in making this distinction, as they are all premenopausal women with normal follicle-stimulating hormone and estradiol levels. The diagnosis of PMS should come from the history relating the occurrence of cyclical mood and behaviour changes with menstruation, the improvement during pregnancy, postnatal depression and the presence of runs of many good days a month and the somatic symptoms of mastalgia, bloating and headaches.

Young women with severe PMS do not respond to the antidepressants and mood-stabilizing drugs typically used for bipolar disorder.